1. Technical Field
This invention relates generally to the field of selective ink curing. More specifically, this invention relates to creating different curing effects on the same print through the use of ultraviolet light-emitting diodes.
2. Description of the Related Art
Digital inkjet printers are used to generate different effects on substrates, such as a glossy surface or highlighting. One way to generate these effects is by using different substrates, such as paper coated with a glossy substance. These substrates, however, cause the entire substrate to show the effect and are more expensive than traditional substrates. FIG. 1A (prior art) is an example of using a matte substrate 100 as a background for printing an object 105. Because the matte substrate 100 applies to the entire background, it cannot be used to highlight specific areas of the substrate, such as text.
As a result of the problems associated with substrates, using a curable inkjet ink to produce the effect is more cost effective and preferable because the effect can be isolated to specific locations. These effects can be produced during ink curing or after the ink has hardened. The ink is typically cured by exposing ink that contains a photoinitiator to ultraviolet (UV) light.
Curable inkjet inks are particularly popular for grand or super-wide format printing systems, which are adapted for billboards, museum displays, billboards, sails, etc. because UV cured inks remain durable on a variety of substrate media.
Printers typically perform UV curing with various light sources, for example, mercury vapor lamps or metal halide bulbs. The problem with these types of various light sources, however, is that they require several minutes after activation to stabilize, they produce excessive heat during curing, ozone is a byproduct of their use, and the light sources have a limited shelf-life.
Another technique for UV curing involves the use of light emitting diodes (LED) that emit UV radiation. UV LEDs are ready to perform curing as soon as they are activated, they require less energy than UV bulbs, and they produce less heat because the LED can be designed to emit a narrow range of wavelengths. U.S. Pat. No. 6,786,589 discloses an ink jet printer in which multiple UV light sources use LEDs to harden the ink drops. U.S. Publication Number 2004/0166249 discloses the use of UV-LED chip arrays to cure inks, where each row in an array can emit a different wavelength of light, but each LED in a row is activated at the same time. In US2006/0119686, each printhead ejector corresponds to one UV-LED and each ink droplet is exposed to the UV-LED exactly once.
FIG. 1B (prior art) illustrates the results of using the UV-LEDs, as taught in these references, to create a matte surface next to an object. Because the UV LEDs are always activated together, the matte is created in all places where a UV curing ink is deposited. Thus, in this example the matte 110 and the object 105 create a matte surface because both inks contain photoinitiators and the entire surface is exposed to the UV-LEDs.
Printers are configured to generate different curing effects using UV ink on a single print by adjusting the UV lamp output to vary the ink curing and surface characteristics. For example, reducing the initial dosage of UV output generates a glossy effect. Increasing the dosage creates a more matte surface. The area can be manipulated by curing once to set the ink and followed with post-dosages to generate different effects.